Hanne Boll

Micro-CT Based Experimental Liver Imaging Using a Nanoparticulate Contrast Agent: A Longitudinal Study in Mice

Background Micro-CT imaging of liver disease in mice relies on high soft tissue contrast to detect small lesions like liver metastases. Purpose of this study was to characterize the localization and time course of contrast enhancement of a nanoparticular alkaline earth metal-based contrast agent (VISCOVER ExiTron nano) developed for small animal liver CT imaging. Methodology ExiTron nano 6000 and ExiTron nano 12000, formulated for liver/spleen imaging and angiography, respectively, were intravenously injected in C57BL/6J-mice. The distribution and time course of contrast enhancement were analysed by repeated micro-CT up to 6 months. Finally, mice developing liver metastases after intrasplenic injection of colon carcinoma cells underwent longitudinal micro-CT imaging after a single injection of ExiTron nano. Principal Findings After a single injection of ExiTron nano the contrast of liver and spleen peaked after 4–8 hours, lasted up to several months and was tolerated well by all mice. In addition, strong contrast enhancement of abdominal and mediastinal lymph nodes and the adrenal glands was observed. Within the first two hours after injection, particularly ExiTron nano 12000 provided pronounced contrast for imaging of vascular structures. ExiTron nano facilitated detection of liver metastases and provided sufficient contrast for longitudinal observation of tumor development over weeks. Conclusions The nanoparticulate contrast agents ExiTron nano 6000 and 12000 provide strong contrast of the liver, spleen, lymph nodes and adrenal glands up to weeks, hereby allowing longitudinal monitoring of pathological processes of these organs in small animals, with ExiTron nano 12000 being particularly optimized for angiography due to its very high initial vessel contrast.

Three-Dimensional In Vivo Imaging of the Murine Liver: A Micro-Computed Tomography-Based Anatomical Study

Various murine models are currently used to study acute and chronic pathological processes of the liver, and the efficacy of novel therapeutic regimens. The increasing availability of high-resolution small animal imaging modalities presents researchers with the opportunity to precisely identify and describe pathological processes of the liver. To meet the demands, the objective of this study was to provide a three-dimensional illustration of the macroscopic anatomical location of the murine liver lobes and hepatic vessels using small animal imaging modalities. We analysed micro-CT images of the murine liver by integrating additional information from the published literature to develop comprehensive illustrations of the macroscopic anatomical features of the murine liver and hepatic vasculature. As a result, we provide updated three-dimensional illustrations of the macroscopic anatomy of the murine liver and hepatic vessels using micro-CT. The information presented here provides researchers working in the field of experimental liver disease with a comprehensive, easily accessable overview of the macroscopic anatomy of the murine liver.

Comparison of Fenestra LC, ExiTron nano 6000, and ExiTron nano 12000 for micro-CT imaging of liver and spleen in mice.

RATIONALE AND OBJECTIVES The purpose of this study was to compare different contrast agents for longitudinal liver and spleen imaging in a mouse model of liver metastasis. MATERIALS AND METHODS Mice developing liver metastases underwent longitudinal micro-computed tomography imaging after injection of Fenestra LC, ExiTron nano 6000, or ExiTron nano 12000. Elimination times and contrast enhancement of liver and spleen were compared. RESULTS For all contrast agents, liver contrast peaked at approximately 4 hours and spleen contrast at 48 hours postinjection. A single dose of 100 μL of ExiTron nano 6000 or 12000 resulted in longstanding enhancement of liver and spleen tissue for longer than 3 weeks, whereas repeated injections of 400 μL of Fenestra LC were required to retain contrast at acceptable levels and allowed imaging of the liver/spleen for up to 2 and 9 days, respectively. CONCLUSION Both ExiTron nano agents provide longer and stronger contrast enhancement of liver and spleen compared to Fenestra LC, and they do so at a 75% lower injection volume in mice.

High-speed single-breath-hold micro-computed tomography of thoracic and abdominal structures in mice using a simplified method for intubation.

Objectives: Respiratory gating with and without controlled ventilation has been applied for in vivo micro-computed tomography (micro-CT) of thoracic and abdominal structures in mice. We describe a simplified method for intubation and demonstrate its applicability for single-breath-hold micro-CT in mice. Methods: Mice (n = 10) were anesthetized, intubated, ventilated, and relaxed by intraperitoneal administration of rocuronium. Contrast-enhanced micro-CT of the complete thorax including the upper abdominal organs (80 kV; 37.5 &mgr;A; 190-degree rotation; 600 projections/20 seconds or 1200 projections/40 seconds; 39 × 39 × 50-&mgr;m voxel size) was performed with and without single-breath-hold technique. Results: The simplified method of intubation was fast (<1 minute) and required no special hardware in all mice. Relaxation of mice allowed prolonged single-breath-hold imaging of up to 40 seconds. Diameter of smallest identifiable lung vessels was 100 &mgr;m. Conclusions: The presented simplified method for intubation in mice is fast, safe, and effective. Additional relaxation allowed high-resolution single-breath-hold micro-CT in mice.

In Vivo X-Ray Digital Subtraction and CT Angiography of the Murine Cerebrovasculature Using an Intra-Arterial Route of Contrast Injection

BACKGROUND AND PURPOSE: Investigation of the anatomy, patency, and blood flow of arterial and venous vessels in small animal models of cerebral ischemia, venous thrombosis, or vasospasm is of major interest. However, due to their small caliber, in vivo examination of these vessels is technically challenging. Using micro-CT, we compared the feasibility of in vivo DSA and CTA of the murine cerebrovasculature using an intra-arterial route of contrast administration. MATERIALS AND METHODS: The ECA was catheterized in 5 C57BL/6J mice. During intra-arterial injection of an iodized contrast agent (30 μL/1 sec), DSA of the intra- and extracranial vessels was performed in mice breathing room air and repeated in hypoxic/hypercapnic mice. Micro-CTA was performed within 20 seconds of intra-arterial contrast injection (220 μL/20 sec). Image quality of both methods was compared. Radiation dose measurements were performed with thermoluminescence dosimeters. RESULTS: Both methods provided high-resolution images of the murine cerebrovasculature, with the smallest identifiable vessel calibers of ≤50 μm. Due to its high temporal resolution of 30 fps, DSA allowed identification of anastomoses between the ICA and ECA by detection of retrograde flow within the superficial temporal artery. Micro-CTA during intra-arterial contrast injection resulted in a reduced injection volume and a higher contrast-to-noise ratio (19.0 ± 1.0) compared with DSA (10.0 ± 1.8) or micro-CTA when using an intravenous injection route (1.3 ± 0.4). CONCLUSIONS: DSA of the murine cerebrovasculature is feasible using micro-CT and allows precise and repeated measurements of the vessel caliber, and changes of the vessel caliber, while providing relevant information on blood flow in vivo.

Implantation of Pipeline Flow-Diverting Stents Reduces Aneurysm Inflow Without Relevantly Affecting Static Intra-aneurysmal Pressure

BACKGROUND Flow-diverting stent (FDS) implantation is an endovascular treatment option for intracranial aneurysms. However, little is known about the hemodynamic effects. OBJECTIVE To assess the effect of stent compression on FDS porosity, to evaluate the influence of single and overlapping implantation of FDS on intra-aneurysmal flow profiles, and to correlate stent porosity with changes in static mean intra-aneurysmal pressure. METHODS Intra-aneurysmal time-density curves were recorded in a pulsatile in vitro flow model before and after implantation of FDSs (Pipeline Embolization Device; ev3) in 7 different types of aneurysm models. Reductions in the maximum contrast inflow and time to maximum intra-aneurysmal contrast were calculated. Micro--computed tomography was performed, and compression-related FDS porosity was measured. The influence of FDS placement on mean static intra-aneurysmal pressure was measured. RESULTS FDS compression resulted in an almost linear reduction in stent porosity. Stent porosity (struts per 1 mm) correlated significantly with the reduction of aneurysm contrast inflow (R = 0.81, P < .001) and delay until maximum contrast (R = 0.34, P = .001). Circulating intra-aneurysmal high-velocity flow was terminated in all sidewall models after implantation of a single stent. Superimposition of 2 stents reduced maximum intra-aneurysmal contrast by 69.1 ± 3.1% (mean ± SD) in narrow-necked sidewall aneurysm models, whereas no substantial reduction in maximum intra-aneurysmal contrast was observed in wide-necked sidewall aneurysm models. Intra-aneurysmal mean static pressure did not correlate with FDS porosity or number of implanted stents. CONCLUSION Implantation of FDS effectively reduces aneurysm inflow in a porosity-dependent way without relevantly affecting static mean intra-aneurysmal pressure. ABBREVIATIONS FDS, flow-diverting stentMAP, mean arterial pressurePED, Pipeline Embolization Device.

Evaluation of a continuous-rotation, high-speed scanning protocol for micro-computed tomography.

Objective: Micro-computed tomography is used frequently in preclinical in vivo research. Limiting factors are radiation dose and long scan times. The purpose of the study was to compare a standard step-and-shoot to a continuous-rotation, high-speed scanning protocol. Methods: Micro-computed tomography of a lead grid phantom and a rat femur was performed using a step-and-shoot and a continuous-rotation protocol. Detail discriminability and image quality were assessed by 3 radiologists. The signal-to-noise ratio and the modulation transfer function were calculated, and volumetric analyses of the femur were performed. The radiation dose of the scan protocols was measured using thermoluminescence dosimeters. Results: The 40-second continuous-rotation protocol allowed a detail discriminability comparable to the step-and-shoot protocol at significantly lower radiation doses. No marked differences in volumetric or qualitative analyses were observed. Conclusions: Continuous-rotation micro-computed tomography significantly reduces scanning time and radiation dose without relevantly reducing image quality compared with a normal step-and-shoot protocol.

Radioimmunoimaging of Liver Metastases with PET Using a 64Cu-Labeled CEA Antibody in Transgenic Mice

Purpose Colorectal cancer is one of the most common forms of cancer, and the development of novel tools for detection and efficient treatment of metastases is needed. One promising approach is the use of radiolabeled antibodies for positron emission tomography (PET) imaging and radioimmunotherapy. Since carcinoembryonic antigen (CEA) is an important target in colorectal cancer, the CEA-specific M5A antibody has been extensively studied in subcutaneous xenograft models; however, the M5A antibody has not yet been tested in advanced models of liver metastases. The aim of this study was to investigate the 64Cu-DOTA-labeled M5A antibody using PET in mice bearing CEA-positive liver metastases. Procedures Mice were injected intrasplenically with CEA-positive C15A.3 or CEA-negative MC38 cells and underwent micro-computed tomography (micro-CT) to monitor the development of liver metastases. After metastases were detected, PET/MRI scans were performed with 64Cu-DOTA-labeled M5A antibodies. H&E staining, immunohistology, and autoradiography were performed to confirm the micro-CT and PET/MRI findings. Results PET/MRI showed that M5A uptake was highest in CEA-positive metastases. The %ID/cm3 (16.5%±6.3%) was significantly increased compared to healthy liver tissue (8.6%±0.9%) and to CEA-negative metastases (5.5%±0.6%). The tumor-to-liver ratio of C15A.3 metastases and healthy liver tissue was 1.9±0.7. Autoradiography and immunostaining confirmed the micro-CT and PET/MRI findings. Conclusion We show here that the 64Cu-DOTA-labeled M5A antibody imaged by PET can detect CEA positive liver metastases and is therefore a potential tool for staging cancer, stratifying the patients or radioimmunotherapy.

A Low Cost Metal-Free Vascular Access Mini-Port for Artifact Free Imaging and Repeated Injections in Mice

Purpose Small injection ports for mice are increasingly used for drug testing or when administering contrast agents. Commercially available mini-ports are expensive single-use items that cause imaging-artifacts. We developed and tested an artifact-free, low-cost, vascular access mini-port (VAMP) for mice. Procedures Leakage testing of the VAMP was conducted with high speed bolus injections of different contrast agents. VAMP-induced artifacts were assessed using a micro-CT and a small animal MRI (9.4T) scanner ex vivo. Repeated contrast administration was performed in vivo. Results With the VAMP there was no evidence of leakage with repeated punctures, high speed bolus contrast injections, and drawing of blood samples. In contrast to the tested commercially available ports, the VAMP did not cause artifacts with MRI or CT imaging. Conclusions The VAMP is an alternative to commercially available mini-ports and has useful applications in animal research involving imaging procedures and contrast agent testing.

Maintained functionality of an implantable radiotelemetric blood pressure and heart rate sensor after magnetic resonance imaging in rats

Radiotelemetric sensors for in vivo assessment of blood pressure and heart rate are widely used in animal research. MRI with implanted sensors is regarded as contraindicated as transmitter malfunction and injury of the animal may be caused. Moreover, artefacts are expected to compromise image evaluation. In vitro, the function of a radiotelemetric sensor (TA11PA-C10, Data Sciences International) after exposure to MRI up to 9.4 T was assessed. The magnetic force of the electromagnetic field on the sensor as well as radiofrequency (RF)-induced sensor heating was analysed. Finally, MRI with an implanted sensor was performed in a rat. Imaging artefacts were analysed at 3.0 and 9.4 T ex vivo and in vivo. Transmitted 24 h blood pressure and heart rate were compared before and after MRI to verify the integrity of the telemetric sensor. The function of the sensor was not altered by MRI up to 9.4 T. The maximum force exerted on the sensor was 273 ± 50 mN. RF-induced heating was ruled out. Artefacts impeded the assessment of the abdomen and thorax in a dead rat, but not of the head and neck. MRI with implanted radiotelemetric sensors is feasible in principal. The tested sensor maintains functionality up to 9.4 T. Artefacts hampered abdominal and throacic imaging in rats, while assessment of the head and neck is possible.